Got a few thousand dollars lying around? If your office is similar to the average U.S. household, you just might. A survey by eBay and Nielsen Customized Research found most of us have 50 unused items around their home that, if sold, could bring in $3,100.

The printer you replaced, the cell phone you upgraded and the book you never read -- it’s time to convert that clutter into cash.

Here are several items just waiting to be turned in for money, and how to cash in.

Donna Smallin Kuper, organizing expert and author of How to De-clutter and Make Money Now (CreateSpace, 2012) says the majority ends up in drawers, “because most people don’t know what to do with their old phones when they get new ones.”

In her book, she lists websites that pay cash for cell phones and other electronics. To sell an old phone, a good place to start is SellCell.com, a price comparison site that gets quotes from multiple buyers. Smallin Kuper also recommends Gazelle.com, a popular site that pays cash for select cell phones as well as iPads, iPods and Macbooks. According to its website, the company has purchased more than a million items, with the average device fetching $125.

Another good site is NextWorth.com, which has one of the most extensive buyback lists. This company will purchase your cell phone, laptop, camera, tablet, e-reader, GPS, television, video game console and even your calculator.

"As soon as I got the iPhone 5, I sold my iPhone 4," she says. "I knew it was worth more at that moment than it ever would be."

Knobloch, founder of Digitwirl.com, recommends selling electronics as soon as you upgrade or decide you don’t need it. And to help with resale value, she suggests taking good care of your gadgets, using a case when possible and skipping the custom engraving.

Books
Most entrepreneurs have a shelf full of books on the latest business trends. Turn them into quick cash by selling to a site that buys books. Start at BookScouter.com, a price comparison site with a database of more than 20 vendors.

Powells is one of the most popular book selling sites. And SellBackBooks.com is a good market for textbooks. Smallin Kuper says she likes this site because of its Android app that lets you scan the ISBN.

Office Equipment and Furnishings
If you have an iPhone, sell office furnishings using the Yardsale iPhone app. Knobloch likes the app because it lets buyers search specific neighborhoods. Other good sites for selling large furnishings include Craigslist.org and Kijiji.com, both of which offer free online classified ads.

Empty Ink Cartridges
Finally, get cash for ink and toner cartridges. TonerBuyer.com buys empty, partially used and new cartridges. Or return empty cartridges to an office supply store, such as Staples or Office Max, and get store credit of $2 per cartridge.

"In our economy, everybody’s looking to make a little extra money," says Knobloch. "Cleaning out the clutter and making extra cash in the process is a great way to do it."